1. Field of the Invention
The present invention relates to an organic EL element lighting device, and to a lighting fixture using the same.
2. Description of the Related Art
Conventionally, organic electroluminescent elements (hereunder called organic EL elements) have been used as surface light sources, and organic EL element lighting devices have been provided for lighting up organic EL elements (see for example Japanese Patent Application Publication No. 2007-93729).
Because organic EL elements are surface light sources, organic EL elements have large capacity components, and are liable to strong surge currents at start-up. These surge currents can damage or shorten the lives of organic EL elements and organic EL element lighting devices. In the above document, surge currents are reduced by inserting an inductor or resistor into the pathway of power supply to the organic EL element, but this creates another problem of increased power loss from the inductor or resistor.
Moreover, in an organic EL element the forward current “If” properties relative to the forward voltage “Vf” (hereunder called the “V-I properties”) as shown in FIG. 12 may vary for each sample or may vary due to environmental factors, such as temperature. As a result, there is a likelihood of start-up variation involving differences in start-up timing and rates of increase in light output. This start-up variation is particularly noticeable when the output voltage is raised gradually, or when fading in during start-up of an organic EL element.